PCI: brcmstb: Don't clk_put() a managed clock

clk_put() was being invoked on a clock obtained by
devm_clk_get_optional().

Link: https://lore.kernel.org/r/20200507201544.43432-2-james.quinlan@broadcom.com
Signed-off-by: Jim Quinlan <jquinlan@broadcom.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>